A prosthetic device for an arm or leg is traditionally worn by inserting the residual limb into a rigid or semi-rigid socket. Traditional sockets are designed as a 360 degree container surrounding the entire residual limb. Sockets generally perform at least two broad functions. Firstly, the traditional socket is designed to allow comfortable weight bearing and prevent soft tissue damage as weight pressures are applied to the residual limb via the prosthetic socket. This is generally achieved with a combination of skeletal weight bearing and hydraulic lift created as the residual limb fluids are pressurized in the socket. Secondly, the traditional socket also functions to stabilize the skeletal components of the residual limb such that the user can move the prosthesis in space and minimize relative motion between the socket and the residual limb.
A precise volumetric fit greatly aids both of these functions. Maintaining a proper amount of volumetric socket fit is challenging and often problematic due to the tendencies of the residual limb to change in volume and the soft tissue to displace under load. Residual limb volume change (RLVC) occurs due to many factors, including but not limited to: edema, muscle atrophy, weight gain/loss, renal dialysis, salt and water intake, alcohol consumption, menses, changes in wearing time and activity. Residual limbs also loose volume daily due to socket pressure and the pumping action of ambulation. Daily volume loss is generally replenished during non-wearing times i.e. sleep, and is cyclical and greatly affected by activity.
As the residual limb loses volume the hydrostatic weight bearing and skeletal control characteristics of the socket are compromised. This leads to painful, limiting and/or injurious increases in socket pressure as well as energy wasting and destabilizing excessive motion between the socket and skeletal segments of the residual limb. As the user attempts to control the prosthesis in space by employing their proximal musculature, relative motion between the residual limb and prosthesis causes forces which accelerate and impact the residual limb. These forces can be compressive, or cause strain or shear, which in turn increase localized pressure and/or tension on the residual limb. This commonly results in pain and injury as well as increased energy use and premature fatigue. As a result, traditional sockets tend not to function well when changes in the residual limb's volume, shape or size occur. This is a common occurrence and has not been addressed effectively.
Additionally, residual limbs are often bulbous in shape with the distal dimensions larger than those more proximal. This shape can cause difficulty in donning the socket because the socket pushes past the larger distal dimension to be secured to the smaller proximal socket dimension
Accordingly, a need exists for a prosthetic limb socket that maintains a proper volumetric fit despite significant volume changes and reduces unwanted relative motion between the residual limb and the prosthesis. Accordingly a need exits for sockets to accommodate bulbous shaped residual limbs.